Kogan Iwamoto (岩本 虎眼 Iwamoto Kogan)
The Grandmaster of the Kogan-Ryuu school. Mentally unbalanced most of the time, he regains his sanity most often in the period between fall and winter. Kogan cares nothing for his daughter, Mie, seeing her only as a tool to continue his bloodline. He has a small deformity, a sixth finger on one of his hands. His technique "Nagare Boshi" (Shooting Star) is known and feared by many Samurai. When he was younger, a Samurai named Yagyuu Munenori, who would later serve as instructor to the House of Shogun tricked Kogan into hiding his extra finger to the son of Tokugawa Ieyasu’s ally Honda Masanobu, knowing full well it would disturb him. This act shattered Kogan’s dreams of serving as instructor to the House of Shogun. Kogan is angered and curses the absence of a son. Kogan does share a tender moment of stating Mie had become beautiful upon being defeated at the hands of Iraku. However, given he envisioned Mie as a bride, it is questionable whether was happy at the sight of his daughter or pleased his daughter would continue his bloodline. Kogan also protects Fujiki from potential death at the hands of Sekiun; but again this could have been to protect his bloodline rather than fearing for Fujiki’s life. Kogan is staunchly constrained by social hierarchy and taught his disciples not to ignore social conventions.
From the outset Iwamoto Kogan is shown to be a formidable swordsman, whose skills are said to be unrivaled in the Noubi area. In his introduction he demonstrates his technique to the lord of Kagegawa, Matsudaira Sadakatsu, by testing a new blade on six criminals, killing all of them with a single strike. "The heads of two out of the six criminals Kogan tested his sword on still remained atop their bodies, even after being cut." it says in the Swordplay Style Founders Record. In the same episode a young Iwamoto Kogan is shown in a sparring match against Yagyu Munenori, who by his own admission stands no chance to defeat Kogan. His mastery of sword-fighting earns him the moniker of Tiger. In another flashback, Kogan tests the veracity of the rumors surrounding the cursed sword named Nana-cho Nenbutsu, which is said to have cut a monk's stomach without causing any blood-loss until said monk walked seven more steps. Iwamoto Kogan executes an unnamed woman, but the real cut is meant for the servant holding her still (a man revealed to have been Iku's lover). The servant is completely unaware of the cut delivered to him, even as Kogan puts the blade back in its scabbard and tells his Lord to watch closely: the servant takes a few more steps and notices a few drops of blood hit the ground and looks down in confusion (seemingly not feeling any pain) only to to see his intestines spill forth from his belly. By the time the main story-line begins, Kogan is already in a state of dementia, but still revered by the students of the Kogan dojo and seemingly unhampered in his combat-skills, as is shown for instance during Irako Seigen's entrance cerimony, when he cuts a small bean on Irako's forehead with an incredibly precise strike, or when he passes a new hand-to-hand technique down to Fujiki, by showing him its effect on a sake bottle. He is able to defeat Sekiun with relative ease, despite being surprised (along with Fujiki and Gonzaemon) by the unusual fighting style employed; Spanish rapier fencing. Kogan deftly catches or parries Sekiun's thrusts, even going so far as to allow himself to be hit by non-deadly blows. Kogan then easily defeats Sekiun with two hand-to-hand blows. In his rage preceding his battle with Irako, he cuts two of his students in half with a sword between the index and middle fingers of each hand (Nagare Toshi or Falling Star). His crowning glory however is his secret technique, the Nagare Boshi (Shooting Star). His prowess as a swordsman extends far beyond mere skill in combat, however, as he seems to have a supernatural link with his swords. He claims to be able to guess, merely by "observing the patterns of a sword's blade [...] how many the sword killed and in what ways. Furthermore, since it is his own instrument, he claims to be able to tell, who takes care of his sword and how he does it, praising Fujiki for his diligence. In the same manner, Kogan is able to determine that his mistress Iku is having an affair with Irako, simply by inspecting her naked body, since she is also his "instrument".